The Molecular Cytogenetics Shared Resource (MCSR) has been in development over the last three years and was formally established as a shared resource in September 2003 to provide a wide range of cytogenetic services and investigations to the OSUCCC research community. It provides state-of-the-art molecular cytogenetic technology as well as classical banded metaphase cytogenetics. Services include metaphase karyotyping of human and mouse tissue, fluorescence in situ hybridization (FISH) using many different types of probes and tissues and multicolor spectral karyotyping (SKY). Dr. Heerema, Director of the Resource, brings a wealth of experience to the MCSR with over 25 years of experience in cytogenetics and over 135 publications. Dr. Mrozek, Associate Director of the Resource, has over 20 years of experience in cytogenetics and over 80 publications. Various specimen sources, such as human and mouse cell lines and tumor samples, paraffin embedded tissues and bone marrow or blood smears are studied, dependent on the purpose of the investigation. Services accommodate different stages of sample preparation from processing fresh tissues to preparing slides from fixed cell suspensions. Probes for FISH studies include both commercially available probes and probes developed by the MCSR. Probe development offerings include growth, amplification and labeling of the probes with different fluorophores available. The types of probes include unique-sequence DNA probes, BACs, PACs and YACs. The MCSR has been widely used by the OSUCCC research community. The projects vary from karyotyping cell lines to development of FISH probes (including probes specific for canine chromosomes), identification of appropriate samples to test the probes and performing FISH on cell lines and archived specimens. From inception to date, 15 OSUCCC members have used the MCSR for 24 different projects representing all six OSUCCC programs and requiring over 2,000 hours of usage. Tools used have included SKY analysis of cell lines and patient samples, G-banded karyotyping of mouse and human tumors and various cell lines, FISH using several different probes and tissues for hybridization as well as development and labeling of some of the probes. An additional 22 projects have been identified for future service. Maintenance of high-standards, establishment and proper use of controls and control values and careful monitoring of all phases of investigation assure quality. It is expected that future use of the MCSR will continue to be extensive, as investigators have indicated continuing need for the services offered.